On loading, potatoes must be
fully mature (sprout dormancy stage) and firm-skinned,
undamaged, sound and of a single variety,
not green, wet or smeared,
free from soil (rot pathogen), organic constituents and stones (otherwise there is insufficient space for airing between the tubers).
It is also necessary to establish that the potatoes have been stored for a specific period postharvest (drying and wound healing period) and are not being loaded while still moist from the soil.
Postharvest, a distinction is drawn between three periods:
drying period (1 - 2 days postharvest):
The tubers must be dried immediately postharvest, to deprive rot pathogens of suitable living conditions and to provide favorable conditions for the subsequent wound healing period. If drying is delayed by just 24 hours, a question mark must be put over its effectiveness. Drying (in the case of storage in heaps) must be performed using the largest possible quantity of air (50 - 100 m3/h) at temperatures 2 - 3°C below stack temperature, although the temperature of the potatoes must not fall below 8°C. If the tubers are covered in a film of water, oxygen depletion occurs, resulting in the risk of rapid rotting. If freshly-harvested potatoes are put into storage straight from the field, they must initially be ventilated continuously for 36 hours, to dry them.
wound healing period (10 - 14 days postharvest):
Injured areas are protected from the penetration of rot-inducing microorganisms by suberization, for which purpose temperatures of 12 - 16°C and relative humidities of 85 - 95% must be ensured. In the event of oxygen depletion and a CO2 content > 0.5%, respiration and thus wound healing are suppressed and the onset of rot is encouraged.
Given the tried and tested method of drying with cooler air than that present in the potato stack and so as to prevent premature sprouting, it is more advisable to allow the wound healing period to proceed at temperatures of 8 - 14°C.
If temperatures are too cool (< 8°C) and the air is too dry, immature, loose-skinned tubers will transpire excessively due to the high permeability of their skin. In the first month after harvest, weight loss (=water loss through transpiration) may amount to 4 - 6%; the tubers become soft and have a greater tendency to blue spots and Fusarium dry rot.
Mature, firm-skinned tubers exhibit only 1 - 3% weight loss due to transpiration.
If potatoes are loaded during the wound healing period, the climatic conditions typical of this period must be taken into account.
Where the temperature is low, the potatoes may heat up by approx. ¼°C per day due to the respiration process. To keep respiration and transpiration losses as low as possible, temperatures of 4 - 6°C and relative humidities of 90 - 95% are deemed best for this period. The reduction in temperature down to the travel temperature must proceed gradually and by no more than 0.5 - 1.0°C/d.
The above-mentioned stages must be taken into account when selecting the travel temperature